Structural components for machinery, such as track links used on the undercarriage of track-type earth moving machines, are required to have material characteristics that include a good yield strength, good wear resistance, good toughness, and good rolling contact fatigue resistance. Track links used on the tracks of a track-type machine such as a bulldozer or other earth moving equipment are well known in the industry.
The manufacturing processes for obtaining the desired material characteristics in a track link or other structural component have typically included hot forging the component from a steel billet, followed by cooling, reheating to austenization temperatures, quenching, and tempering. These heat treatment processes may then be followed by additional heating of at least select portions of the component, quenching again, and tempering again before the final machining. Processing of a track link includes first heating a steel billet to approximately 1150-1350 degrees C. to bring the material to an austenite phase field, and then hot forging billet into a part. The part is then slowly cooled to room temperature, followed by two heat treatment processes. In the first heat treatment process the track link is reheated to austenization temperature, quenched to room temperature, and then tempered to a hardness of approximately 30-39 Rockwell C hardness (HRC). In the second heat treatment process just the rail portion of the track link is locally reheated by induction, quenched to room temperature, and tempered to a hardness of 51-57 HRC. These heat treatment processes result in the track link having a hard rail and a softer body. The body of the link is then machined into final shape. The heat treatment processes add significantly to the expense of producing the components, and also require significant capital expenditures for furnaces, as well as ongoing maintenance expenses.
An alternative process for hardening a forged track chain link having a pad portion, a rail portion, a first side portion and a second side portion is disclosed in U.S. Pat. No. 5,759,309 to K. Watts (“the '309 patent”). The '309 patent discloses a quench tank adapted for spraying one or more of the track chain link portions with a quenchant at a controlled amount of quenchant flow rates, quenchant pressures and quench times. One or more of the track chain link portions are spayed with the quenchant at a controlled amount of one or more of a plurality of quenchant flow rates, a plurality of quenchant pressures and a plurality of quench times. The pad and rail portions are simultaneously hardened to predetermined respective hardnesses.
The steel part produced in accordance with the chemistry and processes of the present disclosure is directed toward overcoming one or more of the problems discovered by the inventors or that is known in the art.